The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2001-269463 filed on Sep. 5, 2001, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an exhaust system for an engine mounted on a small boat, for example, a boat propelled by jet water from a jet pump.
2. Description of Background Art
A jet propulsion boat is a vessel provided with a jet pump mounted at the rear portion of the hull. An engine drives the jet pump to propel the boat by drawing in water from the vessel bottom, and then splashing the water in a rearward direction.
The jet propulsion boat disclosed, for example, in Japanese Patent Laid-Open No. 212936/1998, entitled xe2x80x9cEXHAUST SYSTEM FOR A SMALL PLANING BOATxe2x80x9d, is known. This jet propulsion boat comprises a water muffler disposed midway in the exhaust pipe. FIG. 3 of this patent has been reproduced herein as FIG. 8.
FIG. 8 is a cross sectional view showing the water muffler of the above described related art.
Cooling water used for cooling exhaust gas flows from the insert port 101 of the water muffler 100 into the second chamber 103, as shown by the arrow (a). Then, the cooling water flows from the second chamber 103 flows via the first chamber 102 into the third chamber 104.
On the other hand, exhaust gas discharged from the engine flows from the internal tube 105 of the water muffler 100 into the first chamber 102, as shown by the arrow (b). Exhaust gas from the first chamber 102 flows through a communication cylinder 106 to the second chamber 103, and thereafter, flows through the communication cylinder 107 and into the third chamber 104.
Lastly, the exhaust gas in the third chamber 104, as well as the cooling water which has been trapped in the third chamber 104, flow together out through the exhaust pipe 108.
With this water muffler 100, it is possible to lower exhaust noise to a certain level by flowing exhaust gas into the expansion chambers of the first to third chambers and expanding exhaust gas therein. However, it is difficult to sufficiently eliminate the noise merely by the expansion of gas. Thus, an exhaust system having a sound-deadening resonator disposed in the exhaust pipe has been proposed in order to further lower the noise. Exhaust noise can be lowered by resonating with the resonator.
However, in order to provide a resonator in the exhaust pipe, it is necessary to secure a storing space for storing the resonator in the hull. The interior of the hull of most small boats is limited in size. Thus, in addition to planning for the space required for storing the resonator, consideration must be given to laying out the variety of accessories that also must be mounted in the hull of the vessel. Finding storage space in the hull for all of the required components, in addition to a resonator, has proved to be difficult.
Accordingly, it is an object of the present invention to provide an exhaust system for a small boat that can be stored in a practical manner, which at the same time can achieve the desired reduction in noise.
In order to solve this problem, a first aspect of the present invention provides a small boat in which an exhaust pipe extends rearwardly from the engine provided in the hull. A water muffler is disposed in the exhaust pipe, and exhaust gas is discharged through the water lock pipe in the inverted U-shape extending upward from the water muffler. Further, a resonator chamber for attenuating the resonance of a water lock pipe is provided in the water muffler.
The resonator chamber here refers to a sound box for attenuating resonance of the water lock pipe by utilizing the principle of resonance.
Since the resonator chamber for attenuating resonance of the water lock pipe is provided in the water muffler, it is not necessary to secure a separate storage space for a resonator in the limited space in the hull.
Therefore, the layout of the various accessories required for a vessel can be determined relatively easily.
In addition, by forming the resonator chamber by using a water muffler, the number of the members for constituting the resonator can be reduced. Thus, the resonator can easily be provided, and its cost can be reduced.
In a second aspect of the present invention, an expansion chamber is provided in the water muffler. Further, the extension chamber and the resonator chamber are able to communicate with each other by a communication pipe, the communication pipe being disposed above the level of the cooling water in the water muffler.
The communication pipe which enables the expansion chamber and the resonator chamber to communicate is disposed above the water level in the water muffler. Therefore, since the communication pipe is not closed by cooling water, the expansion chamber and the resonator chamber can freely communicate with each other at all times. Since characteristics of the resonator chamber are maintained, the resonance of the water lock pipe can be attenuated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.